separation of hydrocarbons and hydrocarbon



June l5, 1954 H. c ANDERsoN r-:T AL

OFHYDROCARBONS AND HYDROC'ARBON DERIVATIVES BY ADD 9IRMATION UCT F 20SEPARATION Filed Sept.

N MN JNVENTORS udersam ne felaaey rro/VEY Patented June l5, 1954 UNITEDSTATES PATENT OFFICE SEPARATION OF HYDROCARBONS AND HYDROCARBONDERIVATIVES BY AD- DUCT FORMATION Harry C. Anderson, Baltimore, Md., andCaroline J. Delaney, Mickleton, N. J., assignors to Socony-Vacuum OilCompany, Incorporated, a corporation of New York Application September20, 1949, Serial No. 116,784 9 Claims. (Cl. 196-19) 2 This invention hasto do `with the separation of of aromatic amines containing at least onebasic hydrocarbons and hydrocarbon derivatives of difamino group capableof forming double comferent molecular configuration from mixtures poundswith certain isomeric phenols. It has containing the same. i also beenshown that trans-oestradiol can be separated from the correspondingcis-compound by I FIELD OF INVENTION forming a dihcultly solublecompound of urea and Numerous processes have been developed fortrans-oestradiol (Priewe, 2,300,134).

the Separation of hydrocarbons and hydrocarbon The forces between ureaand the compounds of derivatives of diiierent molecular configuration bythe foregoing complexes are due to specific chemitakingadvantage oftheir selective solubility in 1o cal interaction between the variousfunctional selected reagents or solvents from which they may groups.

later be separated. Exemplary of hydrocarbon One heterocyclic compound,2:6 lutidine, has

separation procedures is the Edeleanu process, been found to form acrystalline compound with solvent refining processes, solventdeasphalting, comparatively few aliphatic hydrocarbon desolvent dewaxingand the like are further exrivatives have been known to date to formcomamples of the separation of hydrocarbons of difplex compounds withurea. In German patent ferent molecular configuration. Typical oiselec-2o application B190,197, IV d/IZ (Technical Oil Mistive solventprocedures for' Separating hydrocarsion, Reel 143; Library of Congress,May 22, 1946),

bon derivatives is the separation of parain wax, Bengen described amethod for the separation of monochlorwax and polychlorwaxes, withacetone aliphatic oxygen-containing compounds (acids, as the selectivesolvent. alcohols, aldehydes, esters and ketones) and of This inventioniS concerned With the general 25 straight chain hydrocarbons of atleastsix carbon eld outlined above. but based 1110011 a different atoms frommixtures containing the same, the and little-known phenomenon, namely,the difmethod being predicated upon the ability of such fering abilityof hydrocarbons and hydrocarbon compounds and hydrocarbons to formAddiderivatives to enter into and to be removed from tionsProdukt," withurea. A mixture containcertain crystalline complexes. As used herein, oing such aliphatic compounds is contacted with the term complex broadlydenotes a combinau a concentrated solution of urea in water, methationof two or more compounds. no1, or ethanol, and the like. In theTechnical Oil This invention is predicated upon the knowl- Missiontranslation of the Bengen application, edge that urea and thiourea formcomplex Crystalhowever, the urea complexes were designated adlnecompounds to a varying degree with various .,5 ducts, which termapparently stems from the forms of hydrocarbons and hydrocarbonderivaanglicized addition product. The adducts tives. are separated intotheir components, urea and Y II. PRIOR ART straight chain hydrocarbon oraliphatic oxygen- For some years it has been known that various@mailling 0011113011101 by heating or by the addiisomers of aromatichydrocarbon derivatives form 4o tion 2f methanol, Water 01' an aqueoussolution. complexes with urea. Kremann (Monatshefte f. ThlOUlea has21150 been kIlOWIl t0 form C0m- Chemie 28, 1125 (1907)) observed thatcomplexes, PleXeS, perhaps the rst of which is a complex with designatedas double compounds, of urea and ethyl oxalate (Nencki, Berichte 7, 780(1874)). the isomer-ic cresols are stable at different tem- Recently,Crystalline IIlOleCUlar Complexes of thioperatures. Schotte and Priewe(1,830,859) later 4. p separated meta-cresol from the correspondingscribed by Ansia (Comptrendus 224, 402-4 and para isomer by selectivelyforming a meta-cresol- 1166 (1947) The organic compounds recited inureacomplex, which was described as an addielude cycllc hydrocarbons such ascyolohexane tion compound; the latter compound was sepacyclohexene,polycyclic terpenes; halides, alcorated from the para isomer and thensplit. up by 5o hols and ketones of such cyclic hydrocarbons; anddistillation or with water or acid to obtain pure halides of short chainparains. Crystalline meta-cresol. The addition compound of metamolecularcomplexes of such compounds are discresol and urea was shown thereafterto have sociated by water and organic solvents to their utility as adisinfectant (Priewe, 1,933,757). components, thiourea and a compound ofthe Bentley and Catlow (1,980,901) found a number 55 foregoing type.

5e III. DEFINITIONS From the foregoing discussion of prior art (II), itwill be clear that a variety of terms have been applied to urea andthiourea complexes. The latter have been rather loosely described asdouble compounds, addition compounds, difcultly soluble compounds,Additions-Produkt, adducts, and crystalline molecular complexes. All ofthese terms are somewhat ambiguous in that they have also been used todescribe products or complexes of different character than the ureacomplexes under consideration. This is particularly so 'with the termadduct, and the related terms unadducted material and non-adductedmaterial. While the term adduct is simple and convenient, it is anunfortunate designation, inasmuch as it confuses these complexes withother substances known in the chemical art. Specifically, adduct hasbeen applied to Diele-Alder reaction products, formed by reactionof'conjugated diolens and olens and their derivatives. As is well known,Diels-Alder products, as a rule do not revert to their originalconstituents when heated or treated with water, acids, solvents, etc.Moreover, the term adduct has been defined earlier as The product of areaction between molecules, which occurs in such a way that the originalmolecules Vor their residues have their long axes parallel to oneanother. (Concise Chemical and Technical Dictionary.) Further ambiguityis introduced by the term adduction which has been defined as oxidation(Hackh.) To avoid the foregoing conflicting terminology, several relatedterms have been coined to dei-lne with greater specificity thesubstances involved in the phenomenon under consideration. Ascontemplated herein and as used throughout the specication and appendedclaims, the following terms identify the phenomenon: Y

Plexad-a revertable associated complex comprising a plexor, such asurea, and at least one other compound; said plexad characterized byreverting or decomposing, under the inuence of heat and/or varioussolvents, to its original constituents, namely, a plexor and at leastone plexand.

Plexan-d--a compound capable of forming a plexad with a plexor, such asurea and thio urea; compounds of this character differ in their capacityto form plexads, depending upon various factors described hereinafter,compounds having a relatively greater capacity for plexation beingidentified as primary plexands, and others being identified as secondaryplexands.

Antiplex-a compound incapable of forming a plexad with a plexor.

Plexor--a compound capable of forming a plexad with a plexand; such asurea and `thiourea.

Plexate-toform a plexad.

Plexation-the act, process or effect of plexating.

IV. OUTLINE OF INVENTION It has 'now been found that the separationprocedures used hitherto can be improved materially to provide a primaryplexand substantially free of a. secondary plexand. More specifically,it has been found that a primary plexand separated, in the form of aplexad, from a mixture of the same and a secondary plexand by plexationand associated with a lesser quantity of the secondary plexand than inthe original mixture, can be further concentrated by treating the (lilplexads with a quantity of depleted plexor sold-1 tion in the presenceof a quantity of the same primary plexand or a different primary plexandhaving a greater capacity to form a plexad than the secondary plexand.In this manner, the secondary plexand is displaced by or exchanged withthe primary plexand.

As indicated above, urea and thiourea plexads have been formed bycontacting a mixture containing plexands and one or more antiplexes,with urea or thiourea carried in a suitable solvent, whereupon urea orthiourea plexads were formed. The plexads were then separated from theantiplex by decantation, filtration or similar means, and the plexadswere decomposed into their components by heating or by contact with asuitable solvent. Plexation procedures of the foregoing character,however, are relatively inefficient when one or more plexands arepresent, inasmuch as an appreciable quantity of the weaker or secondaryplexand is plexated and remains in admixture with the stronger orprimary plexand when the plexads are decomposed. This is particularlypronounced in the treatment of lubricating oil stocks, and of slackwaxesand the like, from which waxes are removed by plexation urea.

By way of illustration, the refining of wax obtained by decomposition ofurea-wax plexads produced by procedures such as mentioned above, hasbeen somewhat difficult and costly because of the high oil content,despite exhaustive washing of the urea plexads with naphthas,liso-octane, pentane or other oil solvents to remove occluded orassociated oil. However, examination of the oil removed from the wax bysolvent reiining methods reveals that the oil is itself capable ofundergoing plexation, and in this sense may be considered as a secondaryplexand having a lesser capacity to form a plexad than the wax, primaryplexand. Further evidence of the ability of the oil to form a ureaplexad is given by its high viscosity index, characteristic ofpredominantly straight-chain hydrocarbons. In

.\ short, then, the oil is not merely mechanically bound or occluded inthe urea plexad, but is, in part at least, actually plexated andtherefore cannot be readily removed by washing with suitable solvents.By the process contemplated herein, however, the oil is effectivelyremoved by contacting the urea plexads with a source of unplexated wax,such as a waxy parain distillate, in the presence of a depleted ureasolution, whereupon the higher molecular weight wax displaces orexchanges with the lower molecular weight plexated oil. This can beeffected in one exchange, or in a series of such exchanges, to reducethe oil content of the wax to a desirable value. In effect, the oilcontent can be reduced such that conventional sweating of the wax isunnecessary, with a refined wax being produced directly by a series ofsuch exchanges.

V. OBJECTS v of this invention to sepsecondary plexand substantiallyfree of a primary plexand.

A more particular object is to separate a primary hydrocarbon plexandfrom other hydrocarbons, including antiplexes and secondary plexands. Animportant object is to separate a hydrocarbon wax from a mixture of thesame and hydrocarbon oils, and to provide a substantially oilfreehydrocarbon l wax.

Another important object is the provision of a continuous method ofseparation of said primary plexands and secondary plexands, which methodis flexiblacapable oi relatively sharp separation, and not highlydemanding of attention and of utilities such as heat, refrigeration.pumping power and the like.

Other objects and advantages of the invention will be apparent from thefollowing description.

VI. INVENTION IN DETAIL As indicated above, it has been found that theforegoing objects are achieved by plexation with urea or thiourea of amixture containing a primary plexand and a secondary p-lexand, therebyforming a mixture of plexads, and treating the plexads in the presenceof tion with the same primary plexand or another 1) PLExANDs ANDMixTUxEs SUITABLE Fon PLEXATION The hydrocarbon mixtures andoxygen-containing paraiin mixtures mentioned in the discussion of theprior art, above, are contemplated herein. So also are the compounds,plexands, shown therein to have the capacity to form plexads. Forexample, when urea is used as a plexor, the mixture used may be:isomeric cresols (Kremann; Schotte and Priewe); oestradiols (Priewe):lutidine-picolines (Riethof); hydrocarbons containing straight chainhydrocarbons of at least six carbon atoms per molecule, andoxygen-containing mixtures containing straight chain acids, alcohols,aldehydes, esters and/or ketones having at least six carbon atoms permolecule (Bengen). It will be apparent from the denitions recited above,that the plexands of these mixtures are the compounds forming plexadswith urea, and compounds which do not form urea plexads.

Hydrocarbon mixtures containing n-parans in the range of Cv-Cao andhigher, such .as wax distillates, foots-oil, gas oils, virgin kerosenes,straight run naphthas` are also suitable when urea is used as theplexor, such mixture being shown in copending application Serial Number4,997, filed January 29, 1948. Other mixtures shown in the latterapplication and also suitable here are: hydrocarbon mixtures containingn-paraiins and n-olerlns, and prepared by synthesis `with carbon`rnonoxide and hydrogen, i. e., typical Fischer-Tropsch productsprepared using cobalt and iron catalysts; cracked mixtures prepared bythe vapor phase cracking of stocks rich in n-paraiiins, such as by thecracking of lparaiinic gas oils, foots-oil, crude waxes, etc.; mixturescontaining straight chain oxygenated compounds, such as acids, alcohols,aldehydes and esters, and containing branched compounds, such as thoseobtained by synthesis from hydrogen and carbon monoxide over an ironcatalyst or by oxidation of high molecular weight hydrocarbons; mixturesconsisting essentially of n-paraffins and n-olefns, for the n-paralinsform stronger plexads than the n-olens; mixtures that the antiplexes arethe consisting essentially of n-oleiins With the double bond in variouspositions, for the oleiins having the double bond near the end of thechain form stronger plexads than those having the double bond furtherfrom the end of the chain; hydrocarbon mixtures obtained byisomerization, alkylation dehydrocyclization, dehydrogenation, etc.

cation Serial Number 374,707, led August 17, 1953. Typical of themixtures described in the latter and 115,730, filed September 13 and 14,194i) respectively, both abandoned, are suitable in the present process.In application Serial No. 115,512, highly branched parains branchedolens are separated from straight As shown in said copending applicationSerial No. 115,511, now abandoned, plexation of a compound, plexand,dissolved in a branched chain (antiplex) with a saturated urea solutionproceeds until the concentrationl of the plexand 1s reduced to a certainminimum concentration which may be termed the equilibrium concentration.In general, the equilibrium concentration is lower, the lower thetemperature `of plexation and is dependent only upon the temperature andnot upon the solvent aes/nece a number of compounds by agitatingsolutions of. varyingv concentrations of various compounds in iso-actanewith` a 70% methanol-30% water solution andnoting the minimumconcentrationv required for plexad formation. The results areVsummarized in Table I below'. These results show that all plexands donot formV plexads equally well, i. e., some plexands, secondary incharacter, form. plexads less readily. For example, it will be notedthat caproic acid forms a plexad more readily than does capryl alcohol,which, in turn, has a greater capacity for plexad formation than eitherthe corresponding chloride or bromide.

Table' I EQUILIBRIUM VALUES In a rsimilar vein, plexation of a plexandwith tion. Normalvdecane-hydrocarbon 'solutions or variousconcentrations of the hydrocarbon beingA investigated were stirred withthioureak solution until the minimum concentration at which plexationwould take place was deiined within 12.5 per cent. The results are shownin Table II, below. Table II EQUILIBIUM VALUES IN THE THIOUREA PLEXATIONOE PARAFFINS AND OLEFIN S Equilibrium Hydrocarbon Temp., C. Conc. inVolume Percent Iso eutane 25. (l 62.5i2.5 2,3- imethyl Butane. 25. 5V29.8172 25. 5 10.7i0 2,2,3-Trlmethyl Butane. 25. 5 11,110.5 D0 25. 583.8113 2,2,4-Trln1ethyl Pentane 25. 5 43.8:l;l.3 Dilsobutylene 25. 032.5:l:2.5

The completeness with which a particular hydrocarbon may be removed bythiourea plexation may be increased by lowering the temperature'. Theequilibrium concentration in an antiplex solvent generally decreases bya iactor of about two (2) in lowering the temperature from 25 C.V to 0C., and by another factor of about 2.3 in lowering the temperature from0 to -25 C'. This relationship is shown by the following. Equilibriumconcentrations for plexad formation of 2,2,3-trimethyl butane anddiisobutylene, respectively. were determined at 0 C. for comparison withthe values at 25 C. The results are given below in Table III.

(2) Pmrxon The plexors used herein include urea and thiourea, each ofwhich is used in solution in a suitable solvent. This solution shouldrange from partially saturated to supersaturated at the temperature atwhich it is contacted with the mixture of plexands, or mixture ofplexands and one or more antiplexes. In some cases, it will be foundconvenient to suspend a further supply of urea a saturated thioureasolution proceeds until the or thiourea crystals in the solution,handling it concentration of the plexand is reduced to a ceras a slurry.The solvent, physically, should have tain minimum concentration, i. e.,,equilibrium at least a slight solvent power for thehydrocarconcentration. This is described in the aiorebons, etc., undertreatment. For gravity or cenmentioned copending application Serial No.trifugal operations, it is convenient to use a sol- 115,512, which wasabandoned together with said vent of such a specific gravity that afterthe forapplication Serial No. 115,730, in favor of said apmation of adesired amount of plexad, the specific plication Serial No. 320,012 (new2,642,378). gravity of the solvent phase will be different fromV When'aplexand in an antiplex solvent is conthat of the plexad phase and of theantiplex tacted with a slurry of thiourea in a saturated phase to adegree sufficient to permit separation thiourea solution, the plexand isplexated to such by gravity, centrifuging, etc. Preferably in such anextent that its concentration is reduced to its.` operations, the ureaor thiourea solvent should equilibrium value for the given temperature,pro have a density less than that of water.

Table III (lEqullilrlim Equiliblrium Il 'l1 Hydrocarbon Vol.(lrerceutlat .Volereltlt B/A AIB 2,2,3-'rrlmethy1 Burana 5.95:;.1 uiotavs 9 ..-=o.53 nusobutyiene usada 32.5'i`2-5 are 'son vided suicientlylong contact times', of the order l The solvent should be substantiallyinert to the compounds of the mixture'and also to the 7G urea andthiourea. Preferably, it should also be singleor multiple-component.

heat stable, both alone and in contact with urea or thiourea, attemperatures at which the desired plexad is not heat stable.

As indicated above, the solvent may be either -It is sometimes Idescribed herein since initial slowly in aqueous media.

Such a solvent, partially to completely saturated with urea or thiourea,lends itself readily to a continuous process for separation byplexation.

In l'certain cases the use of singleecomponent solvents is advantageous.Single-component so1- vents other than alcohols may be employed,although they are normally not as useful as the lower aliphaticalcohols. Glycols may be employed as single solvents, yet ethyleneglycol is generally not suitable in gravity separations due to the highdensity of the urea or thiourea saturated solvent. The higher glycolsand particularly the butylene glycols may be advantageously employed.Diamines such as diamine-ethane, -propane and -butane may likewise beemployed. Additional useful solvents include formic acid, acetic acid,formamide and acetonitrile, although the first three of these aresubject to the same limitations as ethylene glycol.

Other particularly advantageous solvents contemplated herein are theketones described in copending application Serial No. 115,388, ledSeptember 13, 1949, now abandoned and pcreso1 described in copendingapplication Serial No. 115,444, filed September 13, 1949, now U. S.Patent No.2,642,379.

It is, also contemplated herein to include a small quantity of a surfaceactive agent in the urea or thiourea solution, in the manner describedin copending application Serial No. 115,437, led September 13,1949.

Another modification contemplated herein is the procedure serial No.137,739, med January 10,1950, now

abandoned, involving contact of hydrocarbons and/or hydrocarbonderivatives with a plexor impregnated upon a porous support. The use ofwater, or of aqueous plexor solutions, is to be avoided in the plexationand also secondary plexation or exchange occurs quite For efficientoperation, the solvent should be such that plexation and "exchange aresubstantially complete in a relatively short time. In addition, thegreater the volume of plexor solution used, the less agglomerated arethe plexad crystals, and, therefore, the more readily the exchange willoccur inasmuch as plexation and exchange appear to take place in theplexor solvent phase, If the amount of plexor available for plexation isincreased,the amount of material plexated is increased so that, foroptimum operation, relatively dilute plexor solutions are preferred inthe initial plexation and are necessary in the exchange or secondaryplexation. This condition is fulfilled by using all or a portion of theused or depleted plexor solution from the initial plexation in theexchange operation. i

In the exchange operation, the plexor solution used is decient in plexorto cause further plexatio'n. In other words, the depleted or deficientplexor solution from the initial plexation acts as the medium inwhich the exchange is effected, with added primary plexand displacing orexchangingl with the secondary plexand. In this ,exchange noadditionalplexad is formed since the concentration of plexor in the depletedsolution is insucient to form a plexad. In genexchange process eral, thedepleted plexor solutions used in the "exchange operation range fromabout 40 per cent to about 50 per cent of saturation.

The quantity of primary plexand used in the exchange operation, ofnecessity, will vary considerably. This quantity will depend upon theamount of secondary plexand which is in the form of a plexad and whichis to be displaced.

An understanding of a preferred embodiment of this invention may befacilitated by reference to the accompanying illustrative drawing,Figure 1, which is a schematic flow-diagram. of one specic arrangementfor practicing the invention.

In Figure l, a mixture of hydrocarbons such as a paraiiin distillatecontaining wax is introduced through line I to plexation tank 2. Asuitable methanol-urea solution such as one containing 15 to 20 per centby weight urea, is introduced to plexation tank 2 through line 3. Themixture of hydrocarbons and methanol-urea solution in tank 2 is agitatedfor a suitable period of time, from a few minutes to about 3 hours, andat a suitable temperature, for example F., in order to realize asatisfactory degree of plexation. The resulting mixture containingplexads of urea and wax, and of urea and long straight chainhydrocarbons, and containing occluded oil, is taken from tank 2 throughline 4 to lter 5. The plexads are solid and collect on filter plate 6,and the remainder of the mixture from tank 2 is taken as a ltratethrough line 'I to settler 8. In settler 8, methanol-urea solution formsthe upper layer and dewaxed oil, or dewaxed plaran distillate, forms thelower layer and is withdrawn through line 9 for use or for furtherprocessing, such as water-washing and topping to a neutral stock.

The urea plexads collected in filter 5 on plate t are taken through lineI0 to an exchange tank, II, wherein they contact methanolurea solutiontaken from settler 8 through line I2. The methanol-urea solution in lineI2 is, of course,` of lower concentration than that originallyintroduced in line 3, as a consequence of the plexad formation in tank2. Fresh paraiiin distillate containing Wax is also introduced, throughline I3, to exchange tank II and isagitated with the plexads andmethanol-urea solution under conditions of time and temperature such asused in tank 2, or with a higher operating temperature, preferably notabove F. The quantity of fresh parainn distillate introduced throughline I3 is so maintained that there is a deficiency of urea in tank II,that is, insufficient to plexate the long straight chain oils as well asthe wax. In this way, the oils are freed from their corresponding ureaplexads.

The resulting mixture in tank II is taken through line I 4 to lter I 5,wherein the ureawax plexads are collected on lter plate I6. The filtratefrom filter I5 comprises methanol-urea solution and paraffin distillate,and flows through line I1 to settler i8. Methanol-urea solution formsthe upper layer in settler I3 and is taken in part through line I u forrecycle to line 3, and in part through line Ita to decomposition zone22. Parafn distillate of lower wax content than that introduced to thesystem through line I3, forms the lower layer in settler I3 and isrecycled through line 2li to tank 2.

or resolve the plexads, such as about 140 F. The heated mixture in line2| is then introduced to 'settler 23, wherein wax 'forms the upper layerY fresh parafiin distillate in tank Il, it is also advantageous to use awax, carried in a suitable solvent such as a branched chain hydrocarbonor a short chain paraffin. The wax then displaces the'long chain oilsfrom their corresponding urea plexads. Other convenient sources of waxcan also be used in'the exchange, such for example a foots oil.

As a further modification, a multi-stage procedure resembling acounter-current extraction in solvent relining can be employed. Toeffect the exchange of a stronger plexand for a weaker plexand, oil fromone stage is passed forward through a kseries of stages, while bothsolid plexad and urea solution are passed through the series in theopposite direction.

IILUS'IRATIVE: EXAMPLES EXAMPLE I n-Decane (95% purity) and a 20 percent methanol-ureaV solution, were agitated for about minutes at 25 C. Aplexad was formed of urea and n-decane. The plexad was filtered and thesolid plexad was washed twice with n-pentane and dried. A portion of thedried plexand was decomposed on contact with a relatively large quantityof water. The hydrocarbon recovered from the decomposed plexad wasseparated and dried. Upon 'analysis bon had a refractive index (ND-2li)of 1.4108, which is the accepted value for n-decane.

A second portion, 10 parts by weight, of the n-decane-urea plexad wasagitated with a large excess of n-octadecane, 100 parts by weight, andparts by volume of methanol containing urea v(10 parts by weight) at aconcentration insufficient to plexate n-octadecane. [This solution ofurea in methanol was obtained by contacting a saturated solution of ureain methanol with excess n-octadecane and separating therefrom all solidplexadl After stirring the yurea-n-decane plexad, n-octadecane andmethanol-urea solution for three hours at C., theV resulting plexad wasiiltered, washed and vdried asV described above. The plexad so obtainedwas decomposed with water, as indicated above, and the hydrocarbon(plexand) recovered therefrom was dried; an analysis, the hydrocarbonhad a refractive index (NBN) of 1.4831.

Inasmuch as n-decane had a refractive index of 1.4108 and n-octadecanehas a refr-active index (ND32) of 1.4344, it is evident that the re- Ycovered hydrocarbon is predominantly n-cctadecane. Further evidence isprovided in the observation that the recovered hydrocarbon was solid ata temperature of about 20 C. Thus, it is clear that a longer straightchain paraffin will preferentially form a urea plexad than will astraight chain paraflin of fewer carbon atoms.

. ExAMrLE II Pour point, F. 60 Wax (wt. per cent) 8.5 (by solventdewaxing) the recovered hydrocar- Y tion.

12 The plexads formed were .recovered by filtra- One-half ofthe 'plexadswas then decomposed to urea and hydrocarbons with exhaustive washingwith n-pentane at 20-25o C.

One-half of the plexads was agitated for four hours at 2025 C., with 100parts, by voume, of fresh parafn distillate and with 15 parts by volumeof depleted urea solution from the initial plexation. The resultingplexads were recovered by filtration, washed, dried and decomposed inthe same manner as the first plexads. Analyses of the waxes recoveredfrom the initial plexads and from the second plexadsY showed thefollowlng:

. Per cent oil Wax from initial plexads 11.3 Wax from second plexads Theprocedure used for determining oil content is that described at page 972of the October 1948 issue of the Journal of Analytical Chemistry.

EXAMPLE III One hundred and fifty parts, by volume, of a parafndistillate identified in Example II, were agitated for one hour at 20-25C. with 450 parts, by volume, of a saturated urea solution methanol5%t-butanol, solvent). The plexads thus formed were recovered byfiltration. Onethird of the plexads was Washed exhaustively withn-pentane, dried and decomposed, as described in Example I above. Theremainder of the plexads was returned to the same agitator together withthe methanol-urea solution recovered from the initial plexation andparts by volume of fresh paraiiin distillate. The latter materials wereagitated for four hours at 20-25" C. and then .allowed to settle `for 16hours. The resulting plexads were recovered by filtration, and one-halfthereof was washed, vdried and decomposed in the manner described above.

The remainder of the second plexads was Wax exchanged again in themanner used in the second plexation, using the methanol-urea solutionrecovered from the second plexation and using 1'50 parts by volume offresh paraffin distillate. The third plexads were recovered byfiltration, washed, dried and decomposed, in the manner described above.

The oil content of each -of the three waxes recovered from theircorresponding urea plexads are given below:

' Per cent oil Wax before exchange (initial p1exation) 6.1 Wax after oneexchange (second plexati'on) 5.5 Wax after two exchanges (thirdplexaticn) 2.6

We claim:

1. The separation of a compound (I) having the capacity to form acrystalline complex with a complex-forming agent selected from `thegroup consisting of flea and thiourea, from a mixture containing saidcompound (I) and a compound (II) having a lesser capacity to form acrystalline complex withV the same said agent, which comprises:contacting said mixture with a solution containing said agent, underconditions appropriate for the formation of crystalline complexes ofsaid agent and said compounds (I) and (1D separating said crystallinecomplexes Yand depleted solution of said agent; contacting saidcrystalline complexes with ,a quantity of said compound (I) and withaquantity of said depleted solution containing said agent in an amountsufcient to cause further complex formation, whereupon said compound (I)displaces said compound (II) of the crystalline complexes; andseparating a crystalline complex of said agent and said compound (I),from the mixture formed in the last-mentioned operation.

2. The separation of a compound (I) having the capacity to form acrystalline complex with a complex-forming agent selected from the groupconsisting of urea and thiourea, from a mixture containing said compound(I) and a compound (II) having a lesser capacity to form a crystallinecomplex with the same said agent, which comprises: contacting saidmixture with a solution containing said agent, under conditionsappropriate for the formation of crystalline complexes of said agent andsaid compounds (I) and (II); separating said crystalline complexes anddepleted solution of said agent; contacting said crystalline complexeswith a quantity of said compound (I) and with a quantity of saiddepleted solution containing said agent in an amount insuiiicient tocause further complex formation, whereupon said compound (I) displacessaid compound (II) of the crystalline complexes; and separating acrystalline complex of said agent and said compound (I), from themixture formed in the last-mentioned operation; decomposing thecrystalline complex of said agent and said compound (I) to set free saidcompound (I) and said agent; and separating from said agent, saidcompound (I) substantially less contaminated with said compound (II)than said original mixture.

3. The separation the agent is urea.

4. The separation defined by claim 1, wherein the agent is thiourea.

5. The separation of a compound (I) having the capacity to form acrystalline complex with a complex-forming agent selected from the groupconsisting of urea and thiourea, from a mixture containing said compound(I), a compound (II) having a lesser capacity to form a crystallinecomplex with the same said agent, anda compound (III) incapable offorming a crystalline complex with the same said agent, which comprises:contacting said mixture with a solution containing said agent, underconditions appropriate for the formation of crystalline complexes ofsaid agent and said compounds (I) and (II) separating said crystallinecomplexes and depleted solution of said agent, from said compound (III);contacting said crystalline complexes with a quantity of said compound(I) and with a quantity of said depleted solution containing said agentin an amount insunicient to cause further complex formation, whereuponsaid compound (I) displaces said compound (II) of the crystallinecomplexes; and separating a crystalline complex of said agent and saidcompound (I), from the mixture formed in the last-mentioned operation.

6. The separation of a compound (I) having the capacity to form acrystalline complex with a complex-forming agent selected from the groupconsisting of urea and thiourea, from a mixture containing said compound(I), a compound (II) having a lesser capacity to form a crystallinecomplex with the same said agent, and a compound (III) incapable offorming a crystalline defined by claim 1, wherein complex with the samesaid agent, which comprises: contacting said mixture with a solutioncontaining said agent, under conditions appropriate for the formation ofcrystalline complexes of said agent and said compounds (I) and (II)separating said crystalline complexes and depleted solution of saidagent, from said compound (III) contacting said crystalline complexeswith a quantity of said compound (I) and with a quantity of saiddepleted solution containing said agent in an amount insufficient tocause further complex formation, whereupon said compound (I) displacessaid compound (II) of the crystalline complexes; and separating acrystalline complex of said agent and said compound (I), from themixture formed in the lastmentioned operation; decomposing thecrystalline complex of said agent and said compound (I) to set free saidcompound (I) and said agent; and separating from said agent, saidcompound (I) substantially less contaminated with said compounds (II)and (III) than said original mixture 7. The refining of a mixture ofhydrocarbons containing Wax and oil which comprises: contacting saidhydrocarbon mixture with a solution of a urea solvent containing urea,whereupon a mixture of urea-wax and urea-oil crystalline complexes isformed; separating said crystalline complexes and depleted ureasolution; contacting said crystalline complexes with a quantity of saidwax and with a quantity of said depleted urea solution containing ureain an amount insufficient to cause further complex formation, whereuponsaid wax displaces said oil of the urea-oil crystalline complex;separating a ureawax crystalline complex from the mixture formed in thelast-mentioned operation; decomposing the urea-Wax complex to set freewax and urea; and separating from said freed urea, wax substantiallyless contaminated with oil than said hydrocarbon mixture.

8. The rening defined by claim 7, wherein the mixture is a mixture ofsubstantially straight chain hydrocarbons containing wax and oil.

9. The refining of a paranin distillate containing wax and oil, whichcomprises: contacting said distillate with a urea-methanol solution atabout 25 C., whereupon a mixture of urea-wax and urea-oil crystallinecomplexes is formed; separating said crystalline complexes and depletedurea solution; contacting said complexes at about 25 C. with a quantityof fresh parainn distillate and with the depleted urea solution, thelatter containing urea in an amount insuiicient to cause further complexformation, whereupon wax present in said fresh parann distillatedisplaces said oil of the urea-oil crystalline complexes; separating aurea-wax crystalline complex from the mixture formed in thelast-mentioned operation; decomposing said urea-wax complex to set freesaid Wax and urea; and separating from said freed urea, waxsubstantially less contaminated with oil than said parafn distillate.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,376,008 Riethof May 15, 1945 2,464,311 Hiatt et al. Mar. l5,1.949 2,470,339 Clausson et al May 17, 1949 2,499,820 Fetterly Mar. 7,1950 2,549,372 Fetterly II Apr. 17, 1951 2,588,602 Adams et al Mar. ll,1952

1. THE SEPARATION OF A COMPOUND (1) HAVING THE CAPACITY TO FORM ACRYSTALLINE COMPLEX WITH A COMPLEX-FORMING AGENT SELECTED FROM THE GROUPCONSISTING OF UREA AND THIOUREA, FROM A MIXTURE CONTAINING SAID COMPOUND(1) AND A COMPOUND (II) HAVING A LESSER CAPACITY TO FORM A CRYSTALLINECOMPLEX WITH THE SAME SAID AGENT, WHICH COMPRISES: CONTACTING SAIDMIXTURE WITH A SOLUTION CONTAINING SAID AGENT, UNDER CONDITIONSAPPROPRIATE FOR THE FORMATION OF CRYSTALLINE COMPLEXES OF SAID AGENT ANDSAID COMPOUNDS (1) AND (11); SEPARATING SAID CRYSTALLINE COMPLEXES ANDDEPLETED SOLUTION OF SAID AGENT; CONTACTING SAID CRYSTALLINE COMPLEXESWITH A QUANTTITY OF SAID COMPOUND (1) AND WITH A QUANTITY OF SAIDDEPLETED SOLUTION CONTAINING SAID AGENT IN AN AMOUNT SUFFICIENT TO CAUSEFURTHER COMPLEX FORMATION, WHEREUPON SAID COMPOUND (1) DISPLACES SAIDCOMPOUND (11) OF THE CRYSTALLINE COMPLEXES; AND SEPARATING A CRYSTALLINECOMPLEX OF SAID AGENT AND SAID COMPOUND (1), FROM THE MIXTURE FORMED INTHE LAST-MENTIONED OPERATION.